[Paul Tudor Jones], who made a large part of his fortune by calling the infamous stock market crash in October 1987, referred to a chart of the market’s value relative to the country’s economy and said it should be “terrifying” to central bankers, namely Federal Reserve chief Janet Yellen, according to the report.

…The trader said that low interest rates instituted by central bankers around the world have ballooned U.S. stock market valuations back to 2000 levels, right before the dot-com bubble burst and shares plunged.

This chart is sometimes called the “Buffett Indicator” because the Berkshire Hathaway chairman once referred to it in an interview as one of the key measures of valuation he tracks.